The present invention relates to a photomultiplier tube for detecting weak light incident on a faceplate by multiplying electrons emitted on the faceplate, and a method for manufacturing the photomultiplier tube.
Japanese patent Kokai publication No. Hei 5-290793 discloses a conventional photomultiplier tube wherein a hermetically sealed vessel accommodates an electron multiplier. Referring to FIG. 18, a flange 101 is formed over the entire upper end of a metal side tube 100. A lower end face 111a of the flange 101 contacts an upper face 102a of a faceplate 102. The side tube 100 and an upper face 102a of the faceplate 102 are then crimped and welded. Therefore, the flange 101 ensured that the vessel is hermetically sealed.
Heating the side tube 100 is required to weld the side tube to the faceplate. If the side tube 100 has a rectangular section, the amount of heat generated on each of the four corners in the flange 101 is greater than that of the portions other than the corners of the flange 101. As a result, when the flange 101 is fixed to the faceplate 102, a problem may arise that the fixed conditions on the corners are different from those of the portions other than the corners. Accordingly, the problem may affect throughput of manufacturing photomultiplier tubes. Additionally, deformation of the flanges due to heat may result in instability of the hermetic property of the vessel.
An object of the present invention is to provide a photomultiplier tube and a manufacturing method thereof in which the method provides improved throughput, and integration of the side tube and the faceplate are ensured to obtain enhanced hermetic sealing of the vessel.
The present invention features a photomultiplier tube which has a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. The hermetically sealed vessel includes: a stem plate having stem pins for fixing the electron multiplier and the anode thereon; a metal side tube enclosing the electron multiplier and the anode, and having one open end to which the stem plate is fixed; and the faceplate fixed to another open end of the side tube, the faceplate being made of glass. The side tube has a polygonal shape defined by a plurality of plates, each of the plurality of plates having a rolled-up upper end, and the side tube is fused to the faceplate in such a manner that the upper end of each side is embedded in a photocathode side of the faceplate.
In the above photomultiplier tube, the rolled-up edges of the plurality of plates are joined so that the joined plates have a polygonal shape. Each corner, that is, the joint of the plates, is raised more than the other portions. As a result, the upper end of the side tube is more deeply embedded in the faceplate, which contributes to an improved joint condition between the side tube and the faceplate. In addition, the fusion between the side tube and the faceplate is ensured, so that the hermetic seal at the joint portion between the side tube and the faceplate is improved. The throughput of manufacturing the photomultiplier tube is improved.
In the photomultiplier according to present invention, the side tube preferably has an edge portion on the upper end, the edge portion being embedded in a photocathode side of the faceplate. The edge portion provided in the side tube is embedded perpendicularly to the glass faceplate, which contributes to conformability between the side tube and the faceplate and reliability of tight hermetic seal. The edge portion extends upright from the side tube rather than laterally from the side tube like a flange. When the edge portion is embedded as closely as possible to the side face of the faceplate, the effective surface area of the faceplate is increased to nearly 100%. The dead area of the faceplate can be decreased to as nearly 0 as possible.
A tip end of the edge portion of the photemultiplier tube preferably extends straight. This structure enables the edge portion of the side tube to pierce the faceplate. Furthermore, the edge portion is on a line extending from the side tube, which promotes enlargement of the effective sensitive area of the faceplate.
According to present invention, a tip end of the edge portion of the photomultiplier tube may be curved in either one of an interior and an exterior of the side tube. This structure increases a surface area of the edge portion embedded in the faceplate, contributing to improved hermetic seal of the joint between the side tube and the faceplate.
The edge portion of the photomultiplier tube preferably has a knife-edged tip end. This structure enables the edge portion of the side tube to pierce into the faceplate. Therefore, assembly operation and reliability are improved when the glass faceplate is fused to the side tube.
In the photomultiplier tube according to the present invention, it is preferable that an inner side wall at the lower end of the side tube is in contact with an end face of the metal stem plate, then the metal side tube and the metal stem plate are welded together. If this structure is adopted, the side tube and the faceplate are fused together, with an inner side wall at the lower end of the side tube being in contact with an edge face of the stem plate. Therefore, a projection such as a flange is eliminated at the lower end of the photomultiplier tube. Accordingly, it is possible to reduce the external dimensions of the photomultiplier tube, though the above structure of the photomultiplier tube and the side tube may be improper for resistance-welding. When several photomultiplier tubes are arranged, it is possible to place the side tubes closely to each other.
The present invention provides a photomultiplier tube having: a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. The hermetically sealed vessel includes: a stem plate having stem pins for fixing the electron multiplier and the anode thereon; a metal side tube having open ends and enclosing the electron multiplier and the anode, the stem plate being fixed to one of the open ends; and the faceplate fused to the other open end of the side tube, the faceplate being made of glass. The side tube has a cylinder having a polygonal section, the side tube having a plurality of corners, an end face on each of the plurality of corners protrudes beyond an end face of the side tube other than the end faces on the plurality of corners, the faceplate is fused to the other open end so that the other open end is embedded in the photocathode side of the faceplate.
The end face corresponding to the corner at the open end of the side tube facing the faceplate is at a higher level than that of the end face other than the corner. At first, the faceplate is supported by the protruding end face on the corner. Then, melting of the faceplate is started from the supporting position, so that the positional relationship between the side tube and the faceplate is ensured at an early stage of the fusion. Accordingly, the shape of the side tube is readily maintained even during heating.
The present invention features a method for manufacturing a photomultiplier tube having: a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. The photomultiplier tube includes a side tube having a polygonal section with a plurality of plates, each of the plurality of plates having a curled upper end. The method includes the steps of: contacting the upper end on the corner of the side tube to a back surface of the faceplate; and heating the side tube to fuse the upper end of the side tube with the faceplate.
According to the above method, the side tube has a polygonal shape, and is made of a plurality of plates, each of the plates having a curled upper end. When the side tube and the faceplate are assembled, the upper end on a corner of the side tube is first brought into contact with the faceplate. When the side tube is heated, the faceplate starts melting from the corner due to a larger heating value. The melting of the faceplate proceeds toward the center of the plate. Accordingly, the upper end of the corner is fused to the faceplate at first during the early stage of fusing between the faceplate and the heated side tube. The shape of the side tube is maintained while the side tube is heated. The fusing time at the upper end of the corner is longer than the other parts of the upper end. Therefore, the conformability to the glass at the upper end of the corner is improved, thereby avoiding any cracks from occurring at the upper end of the corner. In addition, throughput of manufacturing a photomultiplier tube is improved. The side tube is reliably integral with the faceplate and hermetic sealing of the vessel is enhanced.
The method according to the present invention, an edge portion is provided on the upper end of the side tube, the edge portion is to be embedded into the faceplate. When the above method is adopted, the end of the side tube is easy to be embedded in to the faceplate. And the time required to assemble can be shortened.
According to a method of the present invention, the lower end of the side tube is placed on a rotating platform to force the faceplate onto the side tube. Because the side tube is placed on the rotating platform, un-uniform heating over the side tube during the fusion is reduced. As a result, conformability between the side tube and the faceplate is improved, because the faceplate is pressed to the side tube.
The present invention features a method for manufacturing a photomultiplier tube including: a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. A side tube has a polygonal hollow section and an upper open end and a lower open end. The method includes the steps of: orientating a side tube upright in the manner that an end face on a corner of the upper open end protrudes beyond the end face on the upper end other than the corner; contacting a surface on a photocathode side of the faceplate with an open end face of the upper open end; and heating the side tube to melt a part of the faceplate and fuse the faceplate to the upper end of the side tube while the upper open end of the side tube is embedded into the faceplate.
According to the above method, the positional relation between the side tube and the faceplate is maintained during an early stage of the heating and fusing. The side tube is fused to the faceplate so that the whole open end of the side tube is embedded into the faceplate. Thus, the fusion of the side tube and the faceplate is readily ensured, thereby improving the hermetic seal of the joint between the side tube and the faceplate. In addition, throughput of manufacturing a photomultiplier tube can be improved.